title: Calcium binding to the first EGF-like module of human factor IX in a recombinant fragment containing residues 1-85. Mutations V46E and Q50E each manifest a negligible increase in calcium affinity.
abstract: The first EGF-like module of human coagulation factor IX contains a single functionally important calcium ion binding site. We have now shown the dissociation constant for this site to be approximately 160 microM in a recombinant protein fragment consisting of residues 1-85 in human fIX. This represents a approximately 10-fold increase in affinity as compared with the isolated EGF module (residues 46-85). The Gla module (here with Glu instead of Gla) thus increases the affinity of the EGF module calcium ion binding site. Each of two mutations, V46E and Q50E, made to investigate whether the extra negative charge would increase the affinity of the calcium binding site manifested a negligible increase in affinity.
authors.affiliation: Department of Clinical Chemistry, University of Lund, University Hospital, Malmö, Sweden.
authors.forename: K E
authors.initials: KE
authors.lastname: Persson
authors.forename: J
authors.initials: J
authors.lastname: Astermark
authors.forename: I
authors.initials: I
authors.lastname: Björk
authors.forename: J
authors.initials: J
authors.lastname: Stenflo
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D004815:Epidermal Growth Factor / Q000235:genetics / Q000378:metabolism*; D005164:Factor IX / Q000235:genetics / Q000378:metabolism*; D018698:Glutamic Acid / Q000235:genetics / Q000378:metabolism*; D005973:Glutamine / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D018411:Spodoptera / Q000166:cytology; D014633:Valine / Q000235:genetics / Q000378:metabolism*
chemical_list: D011993:Recombinant Fusion Proteins; D005973:Glutamine; D018698:Glutamic Acid; D004815:Epidermal Growth Factor; D005164:Factor IX; D014633:Valine; D002118:Calcium